Member

Really depends on your switch. Most electric fans pull at least 15 amps, some 20 amps or more, so you'll need your switch to be able to handle that load. Most parts stores carry toggle switches and/or push-pull switches that will handle anywhere from 30-60 amps, so that would work. If you're using one of those thermostatically-controlled deals (or a low amp rated manual switch) you should use a relay.

I have a 30-amp rated push-pull switch on my car. This let me put a decent-looking knob on it too keep it from looking out-of-place on my car.

Member

Be careful about what kind of fuse you are using if you don't run a relay. I used an old style glass "Buss" fuse for a few years without a relay. The fuse was supposedly the correct amperage but it would "de-solder" the ends of the fuse due to the high current load. I converted to a bosch relay and the fusable link from an Audi and have no problem now. I also switched to a sensor from a Chrysler minivan electric fan setup. That turns on the fan at about 185-190. I used the sensor in the ground side of the relay wiring.

Alliance Vendor

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A relay is a REALLY GOOD idea on ANY high amp draw electrical device...

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I completly agree here. Use a relay. I had a electric fan in a '63 ford pickup and I found out he hard way how important a relay is. Left me stranded in the middle of the intersection in town when the fan overloaded everything and I lost power to my ignition. Wire in the relay or have an auto-electric shop do it. It wont cost much and is worth the time and money to do it right.

Member

A relay is great for all the reasons mentioned, but get a high quality one, a cheapie will burn out over time. (contacts are like points contacts, burn up and no longer conduct)

A relay also chews up a little current, too, on top of it all.

A big meaty switch (high amp rating, higher than the fan draws) is a good idea for a failsafe solution, but what I dont like is that you are bringing (thick, hopefully) wires thru the firewall that are carrying a high current load... and assumably these are near the rest of your wiring... In the admittidly odd instance these wires fry, it may take a lot of your electrical system with it....

I say, keep all the high current shit in the engine area, and have the low current stuff running thru the firewall and under the dash... so yeah, thats another vote for a relay.